Definition of chromosomal fragile sites in molecular terms is an essential step towards determining both the mechanism(s) by which fragile sites occur and the relationship (if any) between fragile sites and the specific karyotypic rearrangements associated with cancer, inherited diseases and birth defects. This proposal focuses on the molecular analysis of chromosomal fragile sites induced by the highly oncogenic human adenovirus type 12 (Adl2). Three aspects of Adl2 induced fragile sites will be addressed. First, we will estimate the size of the region disrupted by the Adl2 induced fragile site at 17q2l-q22. These results will be obtained initially on a gross scale from in situ hybridization analysis of the region. Molecular characterization of the region will then be initiated by conducting chromosomal walking experiments starting from the U2 small nuclear RNA gene cluster, a locus that we have shown maps within the disrupted region. Second, we will test the hypothesis that small RNA genes are the target sequences for Adl2 induced chromosome fragility. We propose to determine whether the Ul small nuclear RNA gene locus, which maps at the second most prominent Adl2 fragile site, is disrupted. We also propose to create a new Adl2 fragile site by creating stable transfectants containing a new U2 small RNA gene locus. Finally, we will determine which gene in the Adl2 El region is responsible for inducing specific chromosomal damage. We will assess 17q2l-q22 specific damage in cells either transfected with subclones of the El region or infected with viruses mutated in the El region.